a) Unless you are using a completely fake credit card, they now have all your information.
b) CE and Regular edition will have two separate types of CD Keys as there's still more in-game content you get besides the items you get from the Rave Cards (unless they have a bundle of codes in the box which I doubt it).
If Mythic chooses to, they can have it so that all accounts created using CE Rave card codes will not allow a regular edition CD Key to be registered with it... basically meaning two weeks after launch your account will become inactive until you purchase a copy of the Collectors Edition.
Definitely not saying this is how it's going to happen, but keep it in mind. Would suck to start leveling a character at Head Start only to have to start all over again.
...Oh, yeah, not to mention it's not a nice thing to do....